Center drill



Nov. 23, 1943. F. .Q. SCHWARTZ Patented Nov. 23,, 1943 UNITED STATESPATENT OFFICE CENTRE DRILL Francis Q. Schwartz, Detroit, Mich.Application February 20, 1942, Serial No. 431,620 3 Claims. (Cl. 77-66)The purpose of my improvement is to overcome one of the drawbacksinherent in the design of the conventional drills resulting in theirbreakage while in operation. With this idea in mind, I have-made certainchanges in the form of the drill which, I submit. are new and usefuI. Byreason of said changes, the stresses to which the drill is subjected inoperation are minimized, while that part of the drill which is mostsubjected to torsionai strain while in operation has been considerablystrengthened. Tests conducted by me With the new drill herein describedhave amply proved to me that the danger of breakage has been greatlyreduced. This I have accomplished without making the drill heavier andwithout adversely affecting any of its desirable features.

I shall now describe my improvement'with reference to the accompanyingdrawing, in which Fig. 1 is a side view of my improved drill.

Fig. 2 is a sectional longitudinal view of the drill shown in Fi 1.

Fig. 3 is an end view of the drill shown in vious fi ures.

Fig. 4 is a view similar 150 Fig. 3 drawn on an enlarged scaie andclearly disclosing the space between the curvilinear faces et the flutesand the faces of the truncated cones.

Similar numerals refer to similar parts throughout the several views,

The drill'shown in the above drawing comprises a. shank Il). whichtapers into a truncated cone I l called a head or a. boring head, andwhich in turn supports the drilling member 12 provided with a .wideangle apex la. Il; will be understood that sald head Il, the drillingmember l2, and the apex I3 are axially aligned.

At this juncture I wish to point out that the drilling member l2 is alsomade in the form of a truncated form and not in the form of a cylinder.The feature is important and will be fully appreciated in conjunctionwith flutes 14 with which the drill is provided. The flutes M extendfrom apex l3 upwardly into the body of the shank, as shown, and areseparated by a Web [5. The shape of the flutes. their depth, and themanner of uniform increase of said depth has a bearing on the thicknessof the web, and by reason thereof on the resulting resistance of thedrills to breakage, As for the uniform increase of the depth of theflutes. it is one of the principal features of this invention.

In the conventional center drill construction,

the drilling member 15 cylindrical and where such cylindrlcal portionmarges with the taered porfree ejection of particles of metal cut,insubsquent continuons operation of the drill, inCrease friction betweenthe drill and the body of metal operated upon, and lead to a breakage ofthe drill. Were the fiute to b deepened at this point, it wouldmaterially weaken the web and result in breakage of the drill for thatreason.

The distance between the curvilinear inner faces of the flutes and thejuncture of the truncated drilling member [2 with the truncated cone Ilis never less than the depth of the flutes at any point from the apexportion l3 to the base of the truncated drilling member [2, as isclearly illustrated in Fig. 4 of the drawing. Because of the conicalshape of the drilling member 12, flutes l4 have from their beginning atthe apex l3 to a point close to their nd in the body of the shank, a.uniformly increasing depth without any internal constriction, tighteningor shallowing. On the contrary, the space within the flutes shows agradual expansion in the direction of the shank so that any danger ofpacking of chips within the flutes is eliminated. Simultaneously, theweb is also strengtbened as its thickness increases in continuonsexpansion in the direction away from the apex.

. Apart from the fluting, the drill sboWn by me.

has certain advantages because of the shape alone of the drilling memberl2, which as was pointed out, is' conical in shape. This feature isquite helpful in case the drill, speciflcally the end of the drill,including all or a, part of said drilling member breaks while inoperation and while mbedded in the object worked upon. When the drillingmember is provided with parallel sides as in case of conventionai centerdrills, the grip of the sides of the hole which is being drilled, uponthe drilling member. may be so binding, that in case tlie latter breaks,it is most dificult to remove the broken off part remaining in the hole.In contraSt thereto, the removal of the cone shaped drilling member isquite easy.

Having thus described my improvement, I wish to present thefollowingclaims:

1. A center drill comprising a shank, a drilling head in the form of atruncated cone, a drilling member extending axially from said head andbeing also in the form of a truncated cone, a

ber formed on the lower end of the frusto-conical head and extendingaxlally therefrom, said tool .belng provided with opposed flutesextendng upwardly from the lower end of the drllllng member to a. pointon the shank above the frusto-conloal head, the Inner faces et theflutes being curvilinear, the depth of the flutes at the juncfiure ofthe frusto-conical head with the frusto-conical drfl1ing member belng atleast equal to the depth of the flutes at any point from the lower endof the drflflng member to the base thereot.

3. A tool of the class descflbed comprlslng a. cylindrical shank, a.frusto-ctmlcal head on the lower end thereof, a. frusto-co'nlcaldrflling member formed on the lower end of the truste-coula! head andextending axlally therefrom, a cutflnz apex formd on the lower extremityof the drflflng member, said 12001 being provided w'lth opposed flutesextending upwardly from the lower end of the cutting apex to a point onthe shank above the frustoconical head, the muer faces of the flutesbelng curvllinear, th depth of the flutes at the juncture of thefrusto-conioal head wlth the frusto-conlcal drllllng member belng a.tleast equal to the depth of the flus at. any point from the cutting apexto the baseof the frusto-co'nical drilhng member.

FRANCIS Q. SCHWARIZ.

